This invention relates to the reinforcement of buildings, particularly some time after their original construction.
There are many buildings in the world which are unlikely to stand up when shaken by a substantial earthquake or blasted by a terrorist momb. It is simply not practical to pull all these buildings down and start again, and therefore it is desirable to have some way of reinforcing them, preferably without impairing their appearance or destroying their utility.
Most modern buildings or significant size use reinforced concrete. Typically, there are vertical columns supporting slab floors in a vertical array, forming a basic structure to which cladding and internal partitioning are added later. Once the foundations are laid, a set of columns for the lowermost floor are constructed, the first operating being the setting up of metal cages whose principal members are vertical rods. Generally the columns are square or ractangular, and there is one rod at each corner. Shuttering is then placed around this cage and concrete poured and allowed to set. When all the columns have been completed, the first floor is cast, and there are generally left standing proud of the floor the upper ends of the rods of the initial columns. To these are tied further rods for the next set of columns and so on, storey by storey.
The tying of the rods is never particularly strong, and these are one of the weak points in the building.
There is a known method of reinforcing concrete, masonry and brick structures after construction. It comprises drilling into the structures, inserting a reinforcing rod enveloped by a loose fabric sleeve into the drilling, and injecting grout to expand the sleeve against the wall of the drilling and to penetrate through the fabric to bond to the structure. This will be referred to as the defined method.
The concrete columns in the building described above can be reinforced by this defined method, the centre of each column being generally free of reinforcing rod and therefore susceptible to being drilled without interference. It may also be possible to insert horizontal reinforcements and diagonal ones, across infills between columns. The basic structure can therefore be made substantially stronger than it was originally.
However, windows are a weak point. Ordinary glass shatters quite easily of course, but that problem has largely been overcome by using strengthened or armoured glass. However, this can be more robust than the frame in which it is set, and so the frame has to be upgraded as well. But, in the face of a substantial blast, the whole frame can blow out of the aperture in which it is set. So there is a need to anchor such frames more firmly.
It is the aim of this invention to strengthen buildings in this area.
According to one aspect of the present invention there is provided a method of reinforcing the anchorage of a frame (such as for a door or window) in an aperture in the wall of a building, the method comprising drilling into the reveals of the aperture from within the aperture, the drillings being between the inner and outer faces of the wall, inserting a reinforcing rod enveloped by a loose fabric sleeve into each drilling, leaving an end of the rod secured or securable to a frame within the aperture, and injecting grout to expand the sleeve against the wall of the drilling to penetrate through the fabric and bond to the wall.
Preferably the rod is curved back on itself at the distal end from the frame to form a loop. The loop may be open so that the rod is of thin J-shape, but preferably the rod is of thin U-shape with both ends proximal to and secured or securable to the frame.
In a development of this there can be two such U-shaped rods within the same drilling, one shorter than the other and nested with their planes substantially at right angles. But although that gives added strength, it is not suitable for the interlinking of these anchorages, as outlined below.
When the plane of a single loop anchorage is substantially at right angles to the wall, and when the grout has set, the wall may be drilled between its two faces so that the drill bit passes through the loop. Then an extra reinforcing rod enveloped by a loose fabric sleeve can be inserted in the drilling and grout injected to expand that sleeve against the wall of the drilling, also permeating through the fabric to bond to the wall. And when the aperture has a plurality of looped frame reinforcements along at least one side, the loops can be aligned to receive a common extra reinforcing rod.
Often a structure has an array of apertures with a corresponding set of aligned sides. With each such side having at least one looped frame reinforcement, a common extra reinforcing rod can be passed through all the loops associated with a set of aligned sides. And when there are two parallel arrays of apertures, the looped frame reinforcements of adjacent parallel sets of sides may overlap to be threaded by a common extra reinforcing rod.
However, while tests have suggested that this is an effective method of strengthening the anchorage of window frames and their surrounds, it is not always practical to reinforce a building to such an extent that it can withstand explosions of great power. It would be more sensible to make them resistive up to a certain point, but after that to allow some xe2x80x9cgivexe2x80x9d, to absorb the energy of a blast or seismic jolt by controlled movement.
According to another aspect of the present invention there is provided reinforcing rod for the defined method, the rod being composed of a plurality of sections coupled by energy absorbing means that fail at a predetermined critical load.
When there are more than two sections, the critical loads of the couplings need not be uniform throughout the rod. Some can be arranged to give way earlier than others so that there can be progressive and relatively controlled failure of the structure.
There are several ways of conveniently and economically forming an energy absorbing coupling. For example, two adjacent sections may overlap and be strapped together by an encircling element, or the overlapping portions could be transversely drilled to receive a shear pin. In another arrangement two adjacent sections can hook around a hollow member from opposite directions, this member crumpling when the critical load is applied. A further possibility is for two adjacent sections to hook directly together, at least one hook being designed to straighten and thus release when the critical load is applied.
In yet another further possible arrangement, one of two adjacent sections has a throat through which an end of the other of said two sections passes, that end having an enlargement beyond the throat which normally maintains the sections coupled. But when the critical load is applied the enlargement is capable of forcing its way through the throat.
Although it will generally be the case that the same type of coupling will be used throughout the rod when there are more than two sections, at least one coupling can differ from another, the different couplings being selected for example from those outlined above.
When a wall is reinforced by such a multi-section rod and is non-uniform and has relatively weak and strong portions through which the rod passes, the energy absorbing couplings will generally be in the weak portions. A typical example is a reinforced concrete frame building with brick infills. The couplings would be within the brick to control the disintegration in the face of blast or seismic shock. The frame could be further reinforced using the defined method, the vertical and horizontal members being drilled to receive sleeved reinforcing rods subsequently encased by grout.